In the absence of direct sources of greenhouse gas (GHG) emissions (i.e. combustion), other sources of emission become dominant in so-called 'emission-free' power plants. In this study the indirect GHG emissions, related to construction of nuclear plants, windfarms and photovoltaic plants, are estimated with two different types of life-cycle assessment. The process-chain analysis divides an investment good into its material components (tons of material) and then unravels the entire production process of each material product. The energy required in, and the GHG emissions related to, the construction of the power plant are obtained by integration over all process steps and summation over all material products. The input/output analysis looks at the different economic sectors called on in the construction of the power plant. The sectors that represent a part of the total cost of the power plant are responsible for the amount of energy used (and the corresponding GHG emissions) to deliver their final product. A result is provided by detailed analysis of all relevant sectors and fitting them into the construction phase. Using similar techniques, energy use and GHG emissions related to maintenance and demolition, including storage of nuclear equipment, can be quantified. For construction, maintenance and demolition of these power plants, following orders of magnitude are obtained: nuclear: 40kJ(prim)/kWh(el), 3g(CO2)/kWh(el); wind(coast): 120kJ(prim)/kWh(el), 9g(CO2)/kWh(el); wind(inland): 350kJ(prim)/kWh(el), 25g(CO2)/kWh(el); PV(1998): 3000kJ(prim)/kWh(el), 130g(CO2)/kWh(el); PV(near future): 1500kJ(prim)/kWh(el) and 60g(CO2)/kWh(el).